1. Field of the Invention
The present invention relates generally to cordless telephones. More particularly, the present invention relates to the inclusion of speakerphone features in the remote handset of a digital cordless telephone.
2. Background of Related Art
Typical cordless telephones contain a base unit connected to a telephone line, and a portable unit or remote handset. The base unit and remote handset are coupled via a frequency modulated radio frequency (RF) link. The RF link either transmits the voice signals between the base unit and the remote handset using analog techniques (e.g., frequency modulation (FM), or using digital techniques (e.g., quadrature amplitude modulation (QAM) or frequency shift keying (FSK), etc.).
A speakerphone allows hands-free communication over a telephone line. A speakerphone typically includes a receiving element (e.g., a microphone) to detect voice and other sounds, and a transmitting element (e.g., a loudspeaker) to audibly broadcast sound signals.
As is well known, the placement of a microphone close to a speaker in a closed audio loop can cause annoying feedback, e.g., in the form of whining and wailing noises output from the speaker. To avoid feedback problems, speakerphones typically operate either in half-duplex mode, or in an echo-canceling mode.
In half-duplex mode, a conversation between two parties is carried in one direction at a time, essentially requiring the connected parties to take turns speaking. For example, when one party is transmitting, they cannot at the same time receive voice signals from the other party, and vice versa.
In echo canceling mode, a conversation is carried in both the transmitting and receiving directions simultaneously. Echo cancelers suppress portions of the voice signal that would normally cause feedback.
Speakerphones have been adequately implemented in the remote handset of analog cordless telephones. The short delay caused in the transmission of analog voice signals between the base unit and the corresponding remote handset prove negligible for use either in a half-duplex mode or in an echo canceling mode. In an analog implementation, the entire algorithm is implemented in the base unit, and the speaker and microphone in the remote unit are used to implement a speakerphone in the remote handset instead of the speaker and microphone in the base unit, passing the audio over the RF link, causing an insubstantial delay. However, an implementation of a speakerphone in the remote handset of a digital cordless telephone would face challenges not faced with analog telephone cordless telephones.
For instance, in a half-duplex mode digital speakerphone, the significant round trip delay in the digital communication link between the base unit and the remote handset would cause short bursts of what would appear to be echo at the receiving end due to packets already in the pipeline. A significant portion of these delays is typically caused by the time required to packetize and otherwise format the speech data, and/or by the delays inherent in a low bit rate encoding/decoding device (e.g., a code-excited linear predictive (CELP) device). The round-trip delays in a digital cordless telephone between the base unit and the remote handset are often in the range of 15 to 30 milliseconds or more.
For instance, suppose a speakerphone is implemented in the portable handset of a digital cordless telephone. In a receive mode, a receive signal is output through the speaker of the portable handset. If a transmit break-in occurs wherein the user of the portable handset is given use of the communication link to transmit to the base unit, the transmit and receive signals are mixed at the portable handset for a period of time based on the delay (e.g., 15-30 milliseconds) due to acoustic coupling at the portable handset. This signal mix is sent to the base unit where a switching decision is made. Until this switching decision is made, the received signal will be present at the portable handset. Because of the round trip delay, a few packets transmitted to the far end will contain the receive signal mixed in, which will be perceived at the far end as a short initial burst off echo.
Similarly, in echo canceling mode speakerphones the aforementioned delays must be addressed by the echo canceling algorithms used, also requiring significant memory and processing resources.
There is thus a need for a digital cordless telephone implementing a speakerphone in its portable handset which does not exhibit the disadvantages expected from the implementation of conventional speakerphone techniques in a digital cordless telephone.
In accordance with the principles of the present invention, a digital packet transmitted between a base unit and a remote handset of a digital cordless telephone comprises speakerphone control information adapted to allow speakerphone functionality in the remote handset, and voice data information relating to a telephonic conversation.
A digital cordless telephone in accordance with another aspect of the present invention comprises a base unit comprising a controller, an RF transmitter, and an RF receiver. A remote handset comprises a controller, a speakerphone including a microphone and a speaker, an RF transmitter, and an RF receiver. A digital communication link is coupled between the base unit and the remote handset. The digital communication link is adapted to digitally transmit information packets between the base unit and the remote handset in a half-duplex mode. The information packets comprise voice data and control information, the control information comprising break-in indicia indicating an occurrence of a break-in communication emanating from the microphone of the remote handset or a line-in signal from the base unit.
A digital cordless telephone in accordance with yet another aspect of the present invention comprises a base unit comprising a controller, an RF transmitter, and an RF receiver. A remote handset comprises a controller, a speakerphone including a microphone and a speaker, an RF transmitter, and an RF receiver. A digital communication link is coupled between the base unit and the remote handset. The digital communication link is adapted to digitally transmit information packets between the base unit and the remote handset in a full-duplex echo cancellation mode. The information packets comprise voice data and control information. The control information comprises echo cancellation information indicating an amount of echo cancellation performed by a transmitting one of the base unit and the remote handset.
A method of implementing a speakerphone function in a cordless telephone system in accordance with yet another aspect of the present invention comprises providing a base unit comprising a controller, an RF transmitter, and an RF receiver. A remote handset is provided comprising a controller, a speakerphone including a microphone and a speaker, an RF transmitter, and an RF receiver. A digital communication link is coupled between the base unit and the remote handset. The digital communication link is adapted to digitally transmit information packets between the base unit and the remote handset relating to a speakerphone functionality in the remote handset. Voice data and control information are inserted in the information packets. The control information comprises break-in indicia indicating an occurrence of a break-in communication emanating from the microphone of the remote handset.
A method of transmitting data packets between a base unit and a remote handset of a digital cordless telephone while the remote handset is in a speakerphone mode, in accordance with another aspect of the present invention comprises packetizing voice information relating to a conversation on the digital cordless telephone into a plurality of data packets, and inserting speakerphone control information into each of the plurality of data packets.